In a conventional gas turbine engine, fuel is supplied to the combustor through a nozzle that extends into a swifter. The combustor has a plurality of swirlers. Each swifter is attached to the combustor dome, and the nozzle is separated from the swifter by a bearing plate, a configuration that accommodates thermal growth between the nozzle and the swifter. Axial thermal growth is accommodated by the fit between the nozzle and the passage or bore, through which the nozzle extends in the swifter.
The nozzle is at the end of stem or fuel feed arm that extends through the diffuser case wall and the combustor cowl. The stem provides the only nozzle support and carries the fuel to the nozzle. This diffuser case wall also contains an airflow diffuser, which provides air both to the combustor for the combustion process and around the combustor for cooling. The outer wall has a port through which the stem extends and a flanged area to which the stem is attached, providing the only rigid connection between the nozzle and the combustor. The nozzle, located at the end of the support, typically extends rearward at something approaching a right angle to the support. Owing to the nozzle's extension through the bearing plate and the swifter, installing the nozzle involves some manual dexterity, besides imposing some limitation on the combustor's layout. Generally speaking, the nozzle is removed by moving the stem forward far enough that the nozzle (at the end of the stem) clears the bearing plate and the swifter. Then the stem is removed through an access hole in the diffuser case. Installation follows the reverse sequence. Usual practice is to have a prediffuser in front of the combustor, but it must not be so long that the nozzle cannot be installed or removed, a design factor that limits the effectiveness of the prediffuser.
Some combustor designs reduce the size and complexity of the stem, for instance, the configuration shown in U.S. Pat. No. 4,453,384, which uses a generally straight stem (fuel feed arm).